2 Answers

Glalie evolves from Snorunt starting at level 42. It is one of Snorunt's final forms, the other being Froslass.

A female Snorunt will evolve from Snorunt by normal level up. Frosslass will only evolve from Snorunt via exposure to a Dawn Stone on a female Snorunt.

So your Snorunt offspring (from breeding your Frosslass) will be able to evolve into a Glalie or Froslass. When it has evolved into a Glalie it cannot evolve into a Froslass - they are alternative evolutions, and not part of a linear evolution chain.